Modeling and simulation techniques have been developed for estimating the properties and/or behavior of petroleum fluid in a reservoir. Typically, these techniques employ an equation of state (EOS) model that represents the phase behavior of the petroleum fluid in the reservoir. Once the EOS model is defined, it can be used to assess reservoir connectivity and compartmentalization, as well as to compute a wide array of properties, such as volumetric factors and compressibility, heat capacity, saturation pressure (e.g. bubble point or dew point), and the density of each phase, among others. Downhole fluid analysis techniques can be employed to determine the composition of the petroleum fluid and this compositional data can be used as an input to develop the equation of state models. Asphaltenes are generally the heaviest fraction and the most polar component in a petroleum mixture and can behave differently (e.g., forming molecules, nanoaggregates, or clusters) depending on their concentration within the petroleum fluid. The Flory-Huggins Zuo Equation of State (FHZ EOS) can be employed to account for asphaltene gradients when modeling the phase behavior of petroleum fluid.